Kinetic analysis of the sodium gating current in the squid giant axon.

A critical study has been made of the characteristics of the kinetic components of the sodium gating current in the squid giant axon, of which not less than five can be resolved. In addition to the principal fast component Ig2, there are two components of appreciable size that relax at an intermediate rate, Ig3 alpha and Ig 3 beta. Ig3 alpha has a fast rise, and is present over the whole range of negative test potentials. Ig3 beta is absent below -40 mV, exhibits a delayed onset and disappears on inactivation of the sodium system. There are also two smaller components, Ig1 and Ig4, with very fast and much slower relaxation time constants, respectively.